1. Field of the Invention
This invention is related to 2-substituted piperidine analogs. The analogs are selectively active as antagonists of N-methyl-D-aspartate (NMDA) receptor subtypes. The invention is also directed to the use of 2-substituted piperidine analogs as neuroprotective agents for treating conditions such as stroke, cerebral ischemia, central nervous system trauma, hypoglycemia, anxiety, convulsions, aminoglycoside antibiotics-induced hearing loss, migraine headaches, chronic pain, glaucoma, CMV retinitis, psychosis, urinary incontinence, opioid tolerance or withdrawal, or neuro-degenerative disorders such as lathyrism, Alzheimer""s Disease, Parkinsonism and Huntington""s Disease.
2. Related Background Art
Excessive excitation by neurotransmitters can cause the degeneration and death of neurons. It is believed that this degeneration is in part mediated by the excitotoxic actions of the excitatory amino acids (EAA) glutamate and aspartate at the N-methyl-D-Aspartate (NMDA) receptor. This excitotoxic action is considered responsible for the loss of neurons in cerebrovascular disorders such as cerebral ischemia or cerebral infarction resulting from a range of conditions, such as thromboembolic or hemorrhagic stroke, cerebral vasospasms, hypoglycemia, cardiac arrest, status epilepticus, perinatal asphyxia, anoxia such as from drowning, pulmonary surgery and cerebral trauma, as well as lathyrism, Alzheimer""s Disease, Parkinson""s Disease and Huntington""s Disease.
Various classes of substituted piperidine analogs are known. For example, U.S. Pat. No. 5,036,077 generically discloses piperidine derivatives described by the formula: 
wherein Ar represents a phenyl group substituted by R2, R3 and R4 or a naphth-1-yl or naphth-2-yl group, substituted or unsubstituted by 1 or 2 halogen atoms; X represents an oxygen atom or sulfur atom; R1 represents H or a halogen atom; R2 represents a halogen atom, a trifluoromethyl group, a phenyl group which is unsubstituted or substituted by 1 to 3 halogen atoms, a phenoxy group which is unsubstituted or substituted by 1 to 3 halogen atoms, or a C1-C4 alkyl group and the benzyl group substitutes the piperidine radical in the 2, 3 or 4 position. This reference does not exemplify. 2-substituted piperidines. The piperidines are said to be useful as antimicrobial agents, but there is no disclosure or suggestion of treating disorders responsive to selective NMDA receptor subtype antagonists.
Canadian Patent No. 696,999 is directed to N-(alkylene)aryl-2-substituted piperidines useful as vasodilators which are described by the formula: 
Wherein A is an alkylene group having 2 to 3 carbon atoms. There is no mention of using the compounds of this reference as NMDA receptor antagonists or treating disorders responsive thereto.
PCT International Publication Number WO 93/15052 generically describes compounds that are said to be calcium channel antagonists represented by the formula: 
and the salts thereof, wherein R is C1-8 alkyl(phenyl)p, C2-8 alkenyl(phenyl)p, C2-8 alkynyl(phenyl)p, C3-8 cycloalkyl or C1-8 alkyl C3-8 cycloalkyl;
p is 0 to 2;
n is 0 to 6;
m is 0 to 6;
A is a bond, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x95x90Cxe2x80x94, oxygen, sulphur or NR1;
R1 is hydrogen, C1-8 alkyl or phenyl C1-4 alkyl; and
Ar is aryl or heteroaryl, each of which may be optionally substituted. 2-[2-(3,4-Dichlorophenoxy)ethyl]-1-cinnamylpiperidine oxalate hemihydrate and 4-[2-(2-Dibenzofuranyloxy)ethyl]-1-cinnamylpiperidine oxalate are exemplified. The compounds of this reference are said to be useful for treating anoxia, ischaemia, such as stroke, migraine, epilepsy, traumatic head injury, AIDS-related dementia, neurodegenerative diseases and drug addiction withdrawal. This reference does not disclose or suggest NMDA receptor activity, let alone selective NMDA receptor subtype antagonism.
European Patent Application No. 235,463 generically discloses calcium antagonists represented by the formula 
wherein;
p is zero, one or two;
A is hydrogen, xe2x80x94Oxe2x80x94R1, xe2x80x94Cxe2x89xa1N, 
xe2x80x83xe2x80x94CH2OR1, xe2x80x94CH2NR1R2;
m is zero to six inclusive;
Q is xe2x80x94CHxe2x80x94, xe2x80x94CH2xe2x80x94 or 
d and n are selected from zero or one and the dotted lines represent double bonds which may form consistent with the valence of carbon;
Ar, D and R are selected from the group consisting of 
and in addition, R may have the values: 
xe2x80x83cycloalkyl or loweralkyl, and
D may have additionally the values: 
Ar (CH2)1-4,
X, Y and Z are selected from the group consisting of hydrogen, lower alkyl, halogen, 
z is one or zero with the proviso that z cannot be zero at the same time n is zero when one of the following occurs at the same time that D is phenyl or substituted phenyl: (A)d is hydrogen, (A)d is cyano, (A)d is aminocarbonyl, or a double bond forms between the xcex1 carbon and a carbon of the central heterocyclic amine-ring; R1 is selected from hydrogen, loweralkyl, phenyl and phenylloweralkyl; R2 is selected from loweralkyl, phenyl and phenylloweralkyl; M is a pharmaceutically acceptable metal ion and the pharmaceutically acceptable salts thereof, including acid addition salts, quaternary salts, and hydrates and alcoholates thereof. This reference discloses that such compounds may be useful as coronary vasodilators, antihypertensives, antiarrhythmic, antiallergy, antihistamic and antisecretory agents. No compounds substituted at the 2 position of the piperidine ring are exemplified nor is there any disclosure or suggestions of NMDA antagonistic activity.
U.S. Pat. No. 5,192,799 generically disclosed amines described by the formula: 
wherein R3-R4 can be taken together to form 4- to 8-membered ring and substituted by aryl, benzyl and heteroaryl. No 2-benzylpiperidine was exemplified in this reference. The compounds are said to be useful for the treatment and prevention of heart diseases. But there is no disclosure or suggestion of treating disorders responsive to selective NMDA receptor subtype antagonists.
European patent application No. 649838 generically disclosed cyclized amines described by the formula: 
wherein the nitrogen heterocycles can be 3-8 member rings and substituted in the 2-4 positions. Ar and Arxe2x80x2 are opt. mono or disubstituted phenyl. No 2-benzylpiperidine was exemplified in this reference. The compounds are said to be useful to treat arrhythmia and tachycardia. But there is no disclosure or suggestion of treating disorders responsive to selective NMDA receptor subtype antagonists.
Japanese patent application No. 04217945 disclosed amines described by the formula: 
wherein R4-R5 can be taken together to form 5- to 8-membered ring and substituted by benzyl and phenyl. The compounds are said to be useful as antiulcer agents. But there is no disclosure or suggestion of treating disorders responsive to selective NMDA receptor subtype antagonists.
U.S. Pat. No. 5,169,855 generically discloses disubstituted piperidine ether derivatives for use as antipsychotic agents selective for sigma receptors. Similarly, PCT International Publication No. WO 92/18127 and PCT International Publication No. WO 91/06297 generically disclose N-phthalimidoalkyl piperidines which are useful as antipsychotic agents and which are selective for sigma receptors. However, 2-substituted piperidines are not exemplified by any of these references and there is no mention of NMDA receptor activity.
Numerous references have disclosed piperidine derivatives substituted at the 4 and 3 position for use in a variety of treatments. Such references include, for example, U.S. Pat. No. 3,255,196 (3 and 4-substituted piperidines that are active antitussives and possess analgesic, antiemetic and local anaesthetic properties); U.S. Pat. No. 5,202,346 (4-substituted piperidines that are Class III antiarrhythmic agents); PCT International Publication No. WO 92/02502 (3 and 4-substituted piperidines which are calcium channel blockers expected to be useful in the treatment of anoxia, ischemia including stroke, migraine, epilepsy, traumatic head injury, AIDS-related dementia, neurodegenerative diseases and drug addiction); PCT International Publication No. WO 88/02365 (3 and 4-substituted piperidines that may be useful for treatment of mental disorders accompanying cerebrovascular disease); BE 860701 (4-substituted piperidines for use as vasodilators and xcex2-adrenergic inhibitors); FR 2681319 (4-substituted piperidines for use as neuroprotectors and anticonvulsants); and DE 2939292 (4-substituted piperidines for use as antiallergenic and antiinflammatory agents). None of these references discloses or suggest 2-substituted piperidine analogs or their use as selective NMDA receptor subtype antagonists.
Excitatory amino acid receptor antagonists that block NMDA receptors are recognized for usefulness in the treatment of disorders. NMDA receptors are intimately involved in the phenomenon of excitotoxicity, which may be a critical determinant of outcome of several neurological disorders. Disorders known to be responsive to blockade of the NMDA receptor include acute cerebral ischemia (stroke or cerebral trauma, for example), muscular spasm, convulsive disorders, neuropathic pain and anxiety, and may be a significant causal factor in chronic neurodegenerative disorders such as Parkinson""s disease [T. Klockgether, L. Turski, Ann. Neurol. 34, 585-593 (1993)], human immunodeficiency virus (HIV) related neuronal injury, amyotrophic lateral sclerosis (ALS), Alzheimer""s disease [P. T. Francis, N. R. Sims, A. W. Procter, D. M. Bowen, J. Neurochem. 60 (5), 1589-1604 (1993)] and Huntington""s disease. [See S. Lipton, TINS 16 (12), 527-532 (1993); S. A. Lipton, P. A. Rosenberg, New Eng. J. Med. 330 (9), 613-622 (1994); and C. F. Bigge, Biochem. Pharmacol. 45, 1547-1561 (1993) and references cited therein.]. NMDA receptor antagonists may also be used to prevent tolerance to opiate analgesia or to help control withdrawal symptoms from addictive drugs (Eur. Pat. Appl. 488,959A).
Expression cloning of the first NMDA receptor subunit, NMDAR1 (NR1) in Nakanishi""s lab in 1991 provided an initial view of the molecular structure of the NMDA receptor [Nature 354, 31-37 (1991)]. There are several other structurally related subunits (NMDAR2A through NMDAR2D) that join NR1 in heteromeric assemblies to form the functional ion channel complex of the receptor [Annu. Rev. Neurosci. 17, 31-108 (1994)]. The molecular heterogeneity of NMDA receptors implies a future potential for agents with subtype selective pharmacology.
Many of the properties of native NMDA receptors are seen in recombinant homomeric NR1 receptors. These properties are altered by the NR2 subunits. Recombinant NMDA receptors expressed in Xenopus oocytes have been studied by voltage-clamp recording, as has developmental and regional expression of the mRNAs encoding NMDA receptor subunits. Electrophysiological assays were utilized to characterize the actions of compounds at NMDA receptors expressed in Xenopus oocytes. The compounds were assayed at four subunit combinations of cloned rat NMDA receptors, corresponding to four putative NMDA receptor subtypes [Moriyoshi, et al. Nature 1991, 354, 31-37; Monyer et al, Science 1992, 256, 1217-1221; Kutsuwada et al, Nature 1992, 358, 36-41; Sugihara et al, Biochem. Biophys Res. Commun. 1992, 185, 826-832].
An object of this invention is to provide novel 2-substituted piperidine analogs which function as subtype-selective NMDA receptor antagonists.
A further object of this invention is to provide a pharmaceutical composition containing an effective amount of the 2-substituted piperidine analogs to treat cerebrovascular disorders responsive to the selective blockade of NMDA receptor subtypes.
Another object of this invention is to provide a method of treating disorders responsive to the subtype-selective NMDA receptor antagonists in an animal by administering a pharmaceutically effective amount of 2-substituted piperidine analogs.
This invention relates to novel 2-substituted piperidine analogs represented by the formula (I): 
or a pharmaceutically acceptable salt thereof wherein
Ar1 and Ar2 are independently aryl or a heteroaryl group, either of which may be independently substituted by hydrogen, hydroxy, alkyl, a halogenated alkyl group, halogen, nitro, aryl, aralkyl, amino, a lower alkyl amino group or a lower alkoxy group;
each R1 is independently hydrogen, alkyl or hydroxy;
each R2 is independently hydrogen, alkyl or hydroxy;
X is xe2x80x94CH2xe2x80x94, O, S or NR3, wherein R3 is hydrogen or a lower alkyl group having 1 to 6 carbon atoms;
Y is xe2x80x94CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, O, S or NR3;
m is O, 1 or 2; and
n is 0, 1, 2, 3, 4 or 5,
provided that when m is O and X is xe2x80x94CH2xe2x80x94, or m is 1, R1 is H and X is xe2x80x94CH2xe2x80x94 that either Y is not xe2x80x94CH2xe2x80x94 or at least one of R2 is not hydrogen and further provided that when Y is xe2x80x94Cxe2x95x90Cxe2x80x94 then X is not O.
The compounds of the present invention may exist as optical isomers and the inventive compounds include both the racemic mixtures of such optical isomers as well as the individual entantiomers.
Examples of pharmaceutically acceptable addition salts include inorganic and organic acid addition salts such as the hydrochloride, hydrobromide, phosphate, sulphate, citrate, lactate, tartrate, maleate, fumarate, mandelate, oxalate, and the acetate. Alternatively, pharmaceutically acceptable inorganic and organic base addition salts may be used such as sodium hydroxide, potassium hydroxide, lithium hydroxide and the like.
Halogen is fluorine, chlorine, bromine, or iodine; fluorine, chlorine, and bromine are preferred groups.
Alkyl means a straight or branched chain of from one to six carbon atoms or cyclic alkyl of from three to seven carbon atoms including, but not limited to methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, hexyl, cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.
Aryl means a monocyclic or bicyclic carbocyclic aromatic ring system which can be substituted or unsubstituted, for example, but not limited to phenyl, naphthyl or the like.
Heteroaryl means a monocyclic or bicyclic carbocyclic aromatic ring system substituted by one or more hetero atoms, which can be the same or different, and includes, for example, thienyl, benzo[b]thienyl, naphtho[2,3[b]thienyl, thianthrenyl, furyl, pyranyl, isobenzofuranyl, chromenyl, xanthenyl, phenoxanthiinyl, 2H-pyrrolyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, indolizinyl, isoindolyl, 3H-indolyl, indolyl, indazolyl, purinyl, 4H-quinolizinyl, isoguinolyl, quinolyl, phthalzinyl, naphthyridinyl, quinozalinyl, cinnolinyl, pteridinyl, 5aH-carbozolyl, carbozolyl, xcex2-carbolinyl, phenanthridinyl, acrindinyl, perimidinyl, phenanthrolinyl, phenazinyl, isothiazolyl, phenothiazinyl, isoxazolyl, furazanyl, phenoxazinyl groups, quinoxalinyl, 2,3-dioxoquinoxalinyl, benzimidazolyl, 2-oxobenzimdazolyl and 2-oxindolyl groups.
Aralkyl means any of the alkyl groups defined herein substituted by any of the aryl groups as defined herein.
Halogenated alkyl means any of the alkyl groups defined herein substituted by one or more of the halogen groups defined herein, including but not limited to a trifluoromethyl group.
Lower alkyl amino means any of the alkyl groups defined herein substituted by an amino group.
Lower alkoxy means an alkoxy group containing an alkyl group as defined herein.
The instant invention is also related to a pharmaceutical composition containing the compound defined by formula I in an amount effective to treat cerebrovascular disorders responsive to the selective blockade of NMDA receptor subtypes and a pharmaceutically acceptable carrier. Exemplary disorders responsive to such treatment include cerebral ischemia caused by cerebral trauma, stroke, hypoglycemia, heart attack, and surgery; anxiety; psychosis; schizophrenia; glaucoma; CMV retinitis, urinary incontinence; opioid tolerance of withdrawal; and chronic neurodegenerative disorders such as Huntington""s disease, ALS, Parkinsonism and Alzheimer""s disease. The pharmaceutical composition of this invention may also be employed as an analgesic or for the treatment of epilepsy or migraine headaches.
The invention further relates to a method for treating disorders responsive to the selective blockade of N-methyl-D-aspartate receptor subtypes in an animal suffering thereof which comprises administering in unit dosage form at least one compound represented by the formula: 
or a pharmaceutically acceptable salt thereof wherein
Ar1 and Ar2 are independently aryl or a heteroaryl group, either of which may be independently substituted by hydrogen, hydroxy, alkyl, a halogenated alkyl group, halogen, nitro, aryl, aralkyl, amino, a lower alkyl amino group or a lower alkoxy group;
each R1 is independently hydrogen, alkyl or hydroxy;
each R2 is independently hydrogen, alkyl or hydroxy;
X is xe2x80x94CH2xe2x80x94, O, S or NR3, wherein R3 is hydrogen or a lower alkyl group having 1 to 6 carbon atoms;
Y is xe2x80x94CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, O, S or NR3;
m is O, 1 or 2; and
n is 0, 1, 2, 3, 4 or 5.
The novel 2-substituted piperidine analogs of this invention are represented by previously defined formula (I).
Preferred embodiments of the novel 2-substituted piperidine analogs of this invention are represented by formulae (III-VI). In particular, one embodiment is represented by formula (III) as follows: 
or a pharmaceutically acceptable salt thereof wherein Ar1 and Ar2 are independently aryl or a heteroaryl group, either of which may be independently substituted by hydrogen, hydroxy, alkyl, a halogenated alkyl group, halogen, nitro, aryl, aralkyl, amino, a lower alkyl amino group or a lower alkoxy group;
each R1 is independently hydrogen, alkyl or hydroxy;
each R2 is independently hydrogen, alkyl or hydroxy;
Q is xe2x80x94Cxe2x95x90Cxe2x80x94or xe2x80x94Cxe2x89xa1Cxe2x80x94;
Z is xe2x80x94CH2xe2x80x94, O, S or NR3;
m is 0, 1 or 2; and
n is 0, 1, 2, 3, 4 or 5, provided that when Q is xe2x80x94Cxe2x95x90Cxe2x80x94 then Z is not O.
Two additional embodiments of the novel 2-substituted piperidine analogs of this invention are represented by formulae (IV-V) as follows: 
or a pharmaceutically acceptable salt thereof, or 
or a pharmaceutically acceptable salt thereof, wherein Ar1, Ar2, R1, R2, Z, m and n are the same as previously defined.
Yet another embodiment of the novel compounds of this invention is represented by the formula (VI): 
or a pharmaceutically acceptable salt thereof, wherein Ar1, Ar2, R1, R2, m and n are the same as previously defined and L is xe2x80x94CH2xe2x80x94, O, S or NR3.
Exemplary preferred compounds of formula I include, without limitation:
*2-Benzyl-1-(2-phenoxy)ethylpiperidine;
*2-Benzyl-1-(2- (4-trifluoromethyl)phenoxy)ethylpiperidine;
**2-Benzyl-1-(2-(3-amino)phenoxy)ethylpiperidine
**2-(4-chlorophenyl)methyl-1-(2-(3-amino)phenoxy)ethylpiperidine;
**2-Benzyl-1-(3-phenoxy)propylpiperidine;
*2-Benzyl-1-(3-(4-trifluoromethyl)phenoxy)propylpiperidine;
*2-(4-chlorophenyl)methyl-1-(3-(3-amino)phenoxy)propylpiperidine;
**2-Benzyl-1-(4-phenoxy)butylpiperidine;
*2-Benzyl-1-(4-(3-trifluoromethyl)phenoxy)butylpiperidine;
*2-Benzyl-1-(4-(3-amino)phenoxy)butylpiperidine;
2-Benzyl-1-(4-(2-trifluoromethy)phenoxy)butylpiperidine;
**2-Benzyl-1-(4-(4-trifluoromethyl)phenoxy)butylpiperidine;
**2-Benzyl-1-(4-(3-fluoro)phenoxy)butylpiperidine;
2-Benzyl-1-(3-(3-phenyl)propynyl)piperidine;
*2-Benzyl-1-[3-(4-trifluoromethyl)phenyl)propynyl]piperidine;
*2-(4-chlorophenyl)methyl-1-[4-(3-amino)phenyl)butynyl]piperidine;
**2-Benzyl-1-[2-hydroxy-3-(2-methyl)phenoxy]propylpiperidine;
**2-[(2-Ethoxy)phenoxy]methyl-1-(3-phenoxy)propylpiperidine;
*2-[(2-Ethoxy)phenoxy]methyl-1-(3-(3-amino)phenoxy)propylpiperidine;
*2-[(2-Ethoxy)phenoxy]methyl-1-(3-(4-trifluoromethyl)phenoxy)propylpiperidine;
*2-[(2-Ethoxy)phenoxy]methyl-1-(3-(4-trifluoromethyl)phenyl)propylpiperidine;
**2-Benzyl-1-(5-phenoxypentyl)piperidine;
**2-Benzyl-1-(2-(4-nitrophenoxy)ethyl)piperidine;
**1-(2-(4-Aminophenoxy)ethyl)-2-benzylpiperidine;
**2-Benzyl-1-(2-(4-amino-3-nitrophenoxy)ethyl)piperidine;
**2-Benzyl-1-(2-(2-oxobenzimidazol-5-oxy)ethyl)piperidine;
**2-(4-Chlorobenzyl)-1-(2-(4-fluorophenoxy)ethyl)piperidine;
**2-(4-Chlorobenzyl)-1-(2-(4-hydroxyphenoxy)ethyl)piperidine;
**2-Benzyl-1-(2-(4-hydroxyphenoxy)ethyl)piperidine;
**2-Benzyl-1-(2-(4-hydroxyphenoxy)propyl)piperidine;
**2-Benzyl-1-(2-(4-hydroxyphenoxy)butyl)piperidine; and
2-[(4-chloro)phenoxy]methyl-1-(3-phenoxy)propylpiperidine.
Of the above-listed exemplary compounds, the more preferred compounds are designated * and the most preferred are designated **.
The compounds of this invention may be prepared by methods known to one of ordinary skill in the art or readily adaptable from such known methods without undue experimentation. Starting materials employed for the preparation of the inventive compounds are readily available or the preparation thereof is well within the knowledge and ability of one of ordinary skill.
The invention is also directed to a method for treating disorders responsive to the selective blockade of NMDA receptor subtypes in animals suffering thereof. Particular preferred embodiments of the 2-substituted piperidine analogs for use in the method of this invention are represented by previously defined formulae (III-VI) as well as by the compound represented by formula (II): 
or a pharmaceutically acceptable salt thereof, wherein Ar1, Ar2, R1, R2, m and n are the same as previously defined.
Exemplary preferred compounds that may be employed in the method of this invention include, without limitation:
*1,2-Dibenzylpiperidine;
2-Benzyl-1-(4-fluorophenyl)methylpiperidine;
2-Benzyl-1-(4-trifluoromethylphenyl)methylpiperidine;
*2-(4-chlorophenyl)methyl-1-(4-trifluoromethylphenyl)methylpiperidine;
2-Benzyl-1-(2-phenyl)ethylpiperidine;
2-Benzyl-1-(2-(3-fluoro)phenyl)ethylpiperidine;
*2-Benzyl-1-(2-(4-trifluoromethyl)phenyl)ethylpiperidine;
**2-(4-chlorophenyl)methyl-1-(2-(4-fluoro)phenyl)ethylpiperidine;
**2-(4-chlorophenyl)methyl-1-(2-(3-amino)phenyl)ethylpiperidine;
**2-Benzyl-1-(3-phenyl)propylpiperidine;
*2-Benzyl-1-(3-(4-trifluoromethyl)phenyl)propylpiperidine;
**2-(4-chlorophenyl)methyl-1-(3-(3-trifluoromethyl)phenyl)propylpiperidine;
**2-Benzyl-1-(4-phenyl)butylpiperidine;
*2-Benzyl-1-(4-(3-trifluoromethyl)phenyl)butylpiperidine;
**2-(3,4-dichlorophenyl)methyl-1-(4-(4-trifluoromethyl)phenyl)butylpiperidine;
*2-Benzyl-1-(2-phenoxy)ethylpiperidine;
*2-Benzyl-1-(2-(4-trifluoromethyl)phenoxy)ethylpiperidine;
**2-Benzyl-1-(2-(3-amino)phenoxy)ethylpiperidine
**2-(4-chlorophenyl)methyl-1-(2-(3-amino)phenoxy)ethylpiperidine;
**2-Benzyl-1-(3-phenoxy)propylpiperidine;
*2-Benzyl-1-(3-(4-trifluoromethyl)phenoxy)propylpiperidine;
*2-(4-chlorophenyl)methyl-1-(3-(3-amino)phenoxy)propylpiperidine;
**2-Benzyl-1-(4-phenoxy)butylpiperidine;
*2-Benzyl-1-(4-(3-trifluoromethyl)phenoxy)butylpiperidine;
*2-Benzyl-1-(4-(3-amino)phenoxy)butylpiperidine; 2-Benzyl-1-(4-(2-trifluoromethy)phenoxy)butylpiperidine;
**2-Benzyl-1-(4-(4-trifluoromethyl)phenoxy)butylpiperidine;
**2-Benzyl-1-(4-(3-fluoro)phenoxy)butylpiperidine;
2-Benzyl-1-(3-phenyl)propynyl)piperidine;
*2-Benzyl-1-[3-(4-trifluoromethyl)phenyl)propynyl]piperidine;
*2-(4-chlorophenyl)methyl-1-[4-(4-(3-amino)phenyl)butynyl]piperidine;
**2-Benzyl-1-[2-hydroxy-3-(2-methyl)phenoxy]propylpiperidine;
**2-[(2-Ethoxy)phenoxy]methyl-1-(3-phenoxy)propylpiperidine;
*2-[(2-Ethoxy)phenoxy]methyl-1-(3-(3-amino)phenoxy)propylpiperidine;
*2-[(2-Ethoxy)phenoxy]methyl-1-(3-(4-trifluoromethyl)phenoxy)propylpiperidine;
*2-[(2-Ethoxy)phenoxy]methyl-1-(3-(4-trifluoromethyl)phenyl)propylpiperidine;
**2-Benzyl-1-(5-phenoxypentyl)piperidine;
**2-Benzyl-1-(2-(4-nitrophenoxy)ethyl)piperidine;
**1-(2-(4-Aminophenoxy)ethyl)-2-benzylpiperidine;
**2-Benzyl-1-(2-(4-amino-3-nitrophenoxy)ethyl)piperidine;
**2-Benzyl-1-(2-(2-oxobenzimidazol-5-oxy)ethyl)piperidine;
**2-(4-Chlorobenzyl)-1-(2-(4-fluorophenoxy)ethyl)piperidine;
**2-(4-Chlorobenzyl)-1-(2-(4-hydroxyphenoxy)ethyl)piperidine;
**2-Benzyl-1-(2-(4-hydroxyphenoxy)ethyl)piperidine;
**2-Benzyl-1-(2-(4-hydroxyphenoxy)propyl)piperidine;
**2-Benzyl-1-(2-(4-hydroxyphenoxy)butyl)piperidine; and
2-[(4-chloro)phenoxy]methyl-1-(3-phenoxy)propylpiperidine.
Of the above-listed exemplary compounds, the more preferred compounds for use in the method of this invention are designated * and the most preferred are designated **.
The compounds of the present invention are useful in treating or preventing neuronal loss, neurodegenerative diseases and chronic pain. They are also useful as anticonvulsants and for inducing anesthesia, as well as for treating epilepsy and psychosis. The therapeutic and side effect profiles of selective NMDA receptor subtype antagonists and agonists should be markedly different from the more non-selective types of inhibitors. The subtype-selective analogs of the present invention are expected to exhibit little or no untoward side effects caused by non-selective binding with other receptors, particularly, the PCP and glutamate bindings sites associated with the NMDA receptor. In addition, selectivity for different NMDA receptor subtypes will reduce side effects such as sedation that are common to non-subtype-selective NMDA receptor antagonists. The compounds of the present invention are effective in treating or preventing the adverse consequences of the hyperactivity of the excitatory amino acids, e.g. those which are involved in the NMDA receptor system, by preventing the ligand-gated cation channels from opening and allowing excessive influx of Ca++ into neurons, as occurs during ischemia.
Neurodegenerative diseases which may be treated with the compounds of the present invention include those selected from the group consisting of Alzheimer""s disease, amyotrophic lateral sclerosis, Huntington""s disease, Parkinson""s disease and Down""s syndrome.
The compounds of the present invention find particular utility in the treatment or prevention of neuronal loss associated with multiple strokes which give rise to dementia. After a patient has been diagnosed as suffering from a stroke, the compounds of the present invention may be administered to ameliorate the immediate ischemia and prevent further neuronal damage that may occur from recurrent strokes.
Moreover, the compounds of the present invention are able to cross the blood/brain barrier which makes them particularly useful for treating or preventing conditions involving the central nervous system.
The compounds of the invention find particular utility in treating or preventing the adverse neurological consequences of surgery. For example, coronary bypass surgery requires the use of heart-lung machines which tend to introduce air bubbles into the circulatory system which may lodge in the brain. The presence of such air bubbles robs neuronal tissue of oxygen, resulting in anoxia and ischemia. Pre- or post-surgical administration of the compounds of the present invention will treat or prevent the resulting ischemia. In a preferred embodiment, the compounds of the invention are administered to patients undergoing cardiopulmonary bypass surgery or carotid endarterectomy surgery.
The compounds of the present invention also find utility in treating or preventing chronic pain. Such chronic pain may be the result of surgery, trauma, headache, arthritis, pain from terminal cancer or degenerative diseases. The compounds of the present invention also find particular utility in the treatment of phantom pain that results from amputation of an extremity. In addition to treatment of pain, the compounds of the invention are also expected to be useful in inducing anesthesia, either general or local anesthesia, for example, during surgery.
The subtype-selective NMDA receptor antagonists, agonists and modulators may be tested for in vivo anticonvulsant activity after intraperitoneal or intravenous injection using a number of anticonvulsant tests in mice (audiogenic seizure model in DBA-2 mice, pentylenetetrazol-induced seizures in mice, maximum electroshock seizure test (MES) or NMDA-induced death). The compounds may also be tested in drug discrimination tests in rats trained to discriminate PCP from saline. It is expected that most of the compounds of the present invention will not generalize to PCP at any dose. In addition, it is also expected that none of the compounds will produce a behavioral excitation in locomotor activity tests in the mouse. It is expected that such results will suggest that the subtype-selective NMDA receptor antagonists and agonists of the present invention do not show the PCP-like behavioral side effects that are common to NMDA channel blockers such as MK-801 and PCP or to competitive NMDA antagonists such as CGS 19755.
The subtype-selective NMDA receptor antagonists and agonists are also expected to show potent activity in vivo after intraperitoneal and intravenous injection suggesting that these compounds can penetrate the blood/brain barrier.
Elevated levels of glutamate has been associated with glaucoma. In addition, it has been disclosed that glaucoma management, particularly protection of retinal ganglion cells, can be achieved by administering to a patient a compound capable of reducing glutamate-induced excitotoxicity in a concentration effective to reduce the excitotoxicity. See WO94/13275. Thus, the compounds of the present invention, which are expected to cross the blood-retina barrier, are also expected to be useful in the treatment of glaucoma. Preferably, the invention is directed to the treatment of patients which have primary open-angle glaucoma, chronic closed-angle glaucoma, pseudo doexfoliation, or other types of glaucoma or ocular hypertension. Preferably, the compound is administered over an extended period (e.g. at least six months and preferably at least one year), regardless of the changes in the patient""s intraocular pressure over the period of administration. The compounds of the present invention are also useful in treating CMV retinitis, particularly in combination with antiviral agents. CMV afflicts the ganglion cell layer which may result in higher levels of glutamate. Thus, NMDA receptor antagonists could block retinitis by blocking the toxicity effect of high levels of glutamate.
Aminoglycoside antibiotics have been used successfully in the treatment of serious Gram-negative bacterial infections. However, prolonged treatment with these antibiotics will result in the destruction of sensory hearing cells of the inner ear and consequently, induce permanent loss of hearing. A recent study of Basile, et al. (Nature Medicine, 2: 1338-1344, 1996) indicated that aminoglycosides produce a polyamine-like enhancement of glutamate excitotoxicity through their interaction with the NMDA receptor. Thus, compounds of the present invention with NMDA receptor antagonist activity will be useful in preventing aminoglycoside antibiotics-induced hearing loss by antagonizing their interaction with the receptor.
The compounds of the present invention are useful in treating headaches, in particular, migraine headaches. During migraine attack, a sensory disturbance with unique changes of brain blood flow will result in the development of characteristic migraine auras. Since this unique phenomena has been replicated in animal experiments with cortical-spreading depression (CSD) of Leaxc3x3, A. A. P. J., Neurophysiol. 7:359-390 (1944), CSD is considered an important phenomena in the pathophysiology of migraine with aura (Tepley et al., In: Biomagnetism, eds. S. Williamson, L. Kaufmann, pp. 327-330, Plenum Press, New York (1990)). The CSD is associated with the propagation (2xcx9c6 mm/s) of transient changes in electrical activity which relate to the failure of ion homoestatis in the brain, efflux of excitatory amino acids from the neurons and increased energy metabolism (Lauritzen, M., Acta Neurol. Scand. 76 (Suppl. 113):4-40 (1987)). It has been demonstrated that the initiation of CSD in a variety of animals, including humans, involved the release of glutamate and could be triggered by NMDA (Curtis et al., Nature 191:1010-1011 (1961); and Lauritzen et al., Brain Res. 475:317-327 (1988)). Subtype selective NMDA antagonists will be therapeutically useful for migraine headache because they can block CSD and subsequent pain and because of their expected low side effects, their ability to cross the blood brain barrier and their systemic bioavailability.
Bladder activity is controlled by parasympathetic preganglionic neurons in the sacral spinal cord (DeGroat et al., J. Auton. Nerv. Sys. 3:135-160 (1981)). In humans, it has been shown that the highest density of NMDA receptors in the spinal cord are located at the sacral level, including those areas that putatively contain bladder parasympathetic preganglionic neurons (Shaw et al., Brain Research 539:164-168 (1991)). Because NMDA receptors are excitatory in nature, pharmacological blockade of these receptors would suppress bladder activity. It has been shown that the noncompetitive NMDA receptor antagonist MK801 increased the frequency of micturition in rat (Vera and Nadelhaft, Neuroscience Letters 134:135-138 (1991)). In addition, competitive NMDA receptor antagonists have also been shown to produce a dose-dependent inhibition of bladder and of urethral sphincter activity (U.S. Pat. 5,192,751). Thus, it is anticipated that subtype-selective NMDA receptor antagonists will be effective in the treatment of urinary incontinence mediated by their modulation on the receptor channel activity.
Non-competitive NMDA receptor antagonist MK801 has been shown to be effective in a variety of animal models of anxiety which are highly predictive of human anxiety (Clineschmidt, B. V. et al., Drug Dev. Res. 2:147-163 (1982)). In addition, NMDA receptor glycine site antagonists are shown to be effective in the rat protentiated startle test (Anthony, E. W., Eur. J. Pharmacol. 250:317-324 (1993)) as well as several other animal anxiolytic models (Winslow, J. et al, Eur. J. Pharmacol. 190:11-22 (1990); Dunn, R. et al., Eur. J. Pharmacol. 214:207-214 (1992); and Kehne, J. H. et al, Eur. J. Pharmacol. 193:282-292 (1981)).
Glycine site antagonists, (+) HA-966 and 5,7-dichlorokynurenic acid were found to selectively antagonize d-amphetamine induced stimulation when injected into rat nucleus accumbens but not in striatum (Hutson, P. H. et al., Br. J. Pharmacol. 103:2037-2044 (1991)). Interestingly, (+) HA-966 was also found to block PCP and MK801-induced behavioral arousal (Bristow, L. J. et al., Br. J. Pharmacal, 108:1156-1163 (1993)). These findings suggest that a potential use of NMDA receptor channel modulators, but not channel blockers, as atypical neuroleptics.
It has been shown that in an animal model of Parkinson""s diseasexe2x80x94MPP+ or methamphetamine-induced damage to dopaminergic neuronsxe2x80x94can be inhibited by NMDA receptor antagonists (Rojas et al., Drug Dev. Res. 29:222-226 (1993); and Sonsalla et al, Science 243;398-400 (1989)). In addition, NMDA receptor antagonists have been shown to inhibit haloperidol-induced catalepsy (Schmidt, W. J. et al., Amino Acids 1:225-237 (1991)), increase activity in rodents depleted of monoamines (Carlsson et al., Trends Neurosci. 13:272-276 (1990)) and increase ipsilateral rotation after unilateral substantia nigra lesion in rats (Snell, L. D. et al., J. Pharmacol. Exp. Ther. 235:50-57 (1985)). These are also experimental animal models of Parkinson""s disease. In animal studies, the antiparkinsonian agent amantadine and memantine showed antiparkinsonian-like activity in animals at plasma levels leading to NMDA receptor antagonism (Danysz, W. et al., J. Neural Trans. 7:155-166, (1994)). Thus, it is possible that these antiparkinsonian agents act therapeutically through antagonism of an NMDA receptor. Therefore, the balance of NMDA receptor activity maybe important for the regulation of extrapyramidal function relating to the appearance of parkinsonian symptoms.
It is well known to use opiates, e.g., morphine, in the medical field to alleviate pain. (As used herein, the term xe2x80x9copiatesxe2x80x9d is intended to mean any preparation or derivative of opium, especially the alkaloids naturally contained therein, of which there are about twenty, e.g., morphine, noscapine, codeine, papaverine, and thebaine, and their derivatives.) Unfortunately, with continued use, the body builds up a tolerance for the opiate, and, thus, for continued relief, the patient must be subjected to progressively larger doses. Tolerance develops after both acute and chronic morphine administration (Kornetsky et al., Science 162:1011-1012 (1968); Way et al., J. Pharmacol. Exp Ther. 167:1-8 (1969); Huidobro et al., J. Pharmacol. Exp Ther. 198:318-329 (1976); Lutfy et al., J. Pharmacol. Exp Ther. 256:575-580 (1991)). This, in itself, can be detrimental to the patient""s health. Furthermore, a time can come when the tolerance is substantially complete and the pain killing properties of the drug are no longer effective. Additionally, administration of higher doses of morphine may lead to respiratory depression, causing the patient to stop breathing. Seeking alternative drugs to produce analgesia without development of tolerance or as an adjunct therapy to block tolerance without interference with analgesia is an active area of research.
Recent studies have suggested a modulatory role for the NMDA receptor in morphine tolerance. (Trujillo et al., Science 251:85-87 (1991); Marek et al., Brain Res. 547:77-81 (1991); Tiseo et al., J. Pharmacol. Exp Ther. 264:1090-1096 (1993); Lutfy et al., Brain Res. 616:83-88 (1993); Herman et al., Neuropsychopharmacology 12:269-294 (1995).) Further, it has been reported that NMDA receptor antagonists are useful for inhibiting opioid tolerance and some of the symptoms of opioid withdrawal. Thus, the present invention is also directed to the administration of the compounds described herein to inhibit opiate tolerance and to treat or ameliorate the symptoms of opiate withdrawal by blocking the glycine co-agonist site associated with the NMDA receptor.
Thus, the present invention is directed to compounds having high affinity to a particular NMDA receptor subunit and low affinity to other sites such as dopamine and other catecholamine receptors, and a sites. According to the present invention, those compounds having high binding to a particular NMDA subunit exhibit an IC50 of about 100 xcexcM or less in an NMDA subunit binding assay (see Table 1). Preferably, the compounds of the present invention exhibit a selective subunit IC50 of 10 xcexcM or less. Most preferably, the compounds of the present invention exhibit a selective subunit IC50 of about 1.0 xcexcM or less.
Compositions within the scope of this invention include all compositions wherein the compounds of the present invention are contained in an amount which is effective to achieve its intended purpose. While individual needs vary, determination of optimal ranges of effective amounts of each component is within the skill of the art. Typically, the compounds may be administered to mammals, e.g. humans, orally at a dose of 0.0025 to 50 mg/kg, or an equivalent amount of the pharmaceutically acceptable salt thereof, per day of the body weight of the mammal being treated for anxiety disorders, e.g., generalized anxiety disorder, phobic disorders, obsessional compulsive disorder, panic disorder and post traumatic stress disorders or for schizophrenia or other psychoses. Preferably, about 0.01 to about 10 mg/kg is orally administered to treat or prevent such disorders. For intramuscular injection, the dose is generally about one-half of the oral dose. For example, for treatment or prevention of anxiety, a suitable intramuscular dose would be about 0.0025 to about 15 mg/kg, and most preferably, from about 0.01 to about 10 mg/kg.
In the method of treatment or prevention of neuronal loss in ischemia, brain and spinal cord trauma, hypoxia, hypoglycemia, and surgery, to treat or prevent glaucoma or urinary incontinence, as well as for the treatment of Alzheimer""s disease, amyotrophic lateral sclerosis, Huntington""s disease, Parkinson""s disease and Down""s Syndrome, or in a method of treating a disease in which the pathophysiology of the disorder involves hyperactivity of the excitatory amino acids or NMDA receptor-ion channel related neurotoxicity, the pharmaceutical compositions of the invention may comprise the compounds of the present invention at a unit dose level of about 0.01 to about 50 mg/kg of body weight, or an equivalent amount of the pharmaceutically acceptable salt thereof, on a regimen of 1-4 times per day. When used to treat chronic pain, migrane headache, to induce anesthesia, to treat or prevent opiate tolerance or to treat opiate withdrawal, the compounds of the invention may be administered at a unit dosage level of from about 0.01 to about 50 mg/kg of body weight, or an equivalent amount of the pharmaceutically acceptable salt thereof, on a regimen of 1-4 times per day. Of course, it is understood that the exact treatment level will depend upon the case history of the animal, e.g., human being, that is treated. The precise treatment level can be determined by one of ordinary skill in the art without undue experimentation.
The unit oral dose may comprise from about 0.01 to about 50 mg, preferably about 0.1 to about 10 mg of the compound. The unit dose may be administered one or more times daily as one or more tablets each containing from about 0.1 to about 10, conveniently about 0.25 to 50 mg of the compound or its solvates.
In addition to administering the compound as a raw chemical, the compounds of the invention may be administered as part of a pharmaceutical preparation containing suitable pharmaceutically acceptable carriers comprising excipients and auxiliaries which facilitate processing of the compounds into preparations which can be used pharmaceutically. Preferably, the preparations, particularly those preparations which can be administered orally and which can be used for the preferred type of administration, such as tablets, dragees, and capsules, and also preparations which can be administered rectally, such as suppositories, as well as suitable solutions for administration by injection or orally, contain from about 0.01 to 99 percent, preferably from about 0.25 to 75 percent of active compound(s), together with the excipient.
Also included within the scope of the present invention are the non-toxic pharmaceutically acceptable salts of the compounds of the present invention. Acid addition salts are formed by mixing a solution of the particular selective NMDA receptor subtype antagonist or agonist of the present invention with a solution of a pharmaceutically acceptable non-toxic acid such as hydrochloric acid, fumaric acid, maleic acid, succinic acid, acetic acid, citric acid, tartaric acid, carbonic acid, phosphoric acid, oxalic acid, and the like. Basic salts are formed by mixing a solution of the particular 2-substituted piperidine analog of the present invention with a solution of a pharmaceutically acceptable non-toxic base such as sodium hydroxide, potassium hydroxide, choline hydroxide, sodium carbonate and the like.
The pharmaceutical compositions of the invention may be administered to any animal which may experience the beneficial effects of the compounds of the invention. Foremost among such animals are mammals, e.g., humans, although the invention is not intended to be so limited.
The pharmaceutical compositions of the present invention may be administered by any means that achieve their intended purpose. For example, administration may be by parenteral, subcutaneous, intravenous, intramuscular, intraperitoneal, transdermal, or buccal routes. Alternatively, or concurrently, administration may be by the oral route. The dosage administered will be dependent upon the age, health, and weight of the recipient, kind of concurrent treatment, if any, frequency of treatment, and the nature of the effect desired.
The pharmaceutical preparations of the present invention are manufactured in a manner which is itself known, for example, by means of conventional mixing, granulating, dragee-making, dissolving, or lyophilizing processes. Thus, pharmaceutical preparations for oral use can be obtained by combining the active compounds with solid excipients, optionally grinding the resulting mixture and processing the mixture of granules, after adding suitable auxiliaries, if desired or necessary, to obtain tablets or dragee cores.
Suitable excipients are, in particular, fillers such as saccharides, for example lactose or sucrose, mannitol or sorbitol, cellulose preparations and/or calcium phosphates, for example tricalcium phosphate or calcium hydrogen phosphate, as well as binders such as starch paste, using, for example, maize starch, wheat starch, rice starch, potato starch, gelatin, tragacanth, methyl cellulose hydroxypropylmethylcellulose, sodium carboxymethylcellulose, and/or polyvinyl pyrrolidone. If desired, disintegrating agents may be added such as the above-mentioned starches and also carboxymethyl-starch, cross-linked polyvinyl pyrrolidone, agar, or alginic acid or a salt thereof, such as sodium alginate. Auxiliaries include, without limitation, flow-regulating agents and lubricants, for example, silica, talc, stearic acid or salts thereof, such as magnesium stearate or calcium stearate, and/or polyethylene glycol. Dragee cores are provided with suitable coatings which, if desired, are resistant to gastric juices. For this purpose, concentrated saccharide solutions may be used, which may optionally contain gum arabic, talc, polyvinyl pyrrolidone, polyethylene glycol and/or titanium dioxide, lacquer solutions and suitable organic solvents or solvent mixtures. In order to produce coatings resistant to gastric juices, solutions of suitable cellulose preparations such as acetyl-cellulose phthalate or hydroxypropymethyl-cellulose phthalate, are used. Dye stuffs or pigments may be added to the tablets or dragee coatings, for example, for identification or in order to characterize combinations of active compound doses.
Other pharmaceutical preparations which can be used orally include push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a plasticizer such as glycerol or sorbitol. The push-fit capsules can contain the active compounds in the form of granules which may be mixed with fillers such as lactose, binders such as starches, and/or lubricants such as talc or magnesium stearate and, optionally, stabilizers. In soft capsules, the active compounds are preferably dissolved or suspended in suitable liquids, such as fatty oils, or liquid paraffin. In addition, stabilizers may be added.
Possible pharmaceutical preparations which can be used rectally include, for example, suppositories, which consist of a combination of one or more of the active compounds with a suppository base. Suitable suppository bases are, for example, natural or synthetic triglycerides, or paraffin hydrocarbons. In addition, it is also possible to use gelatin rectal capsules which consist of a combination of the active compounds with a base. Possible base materials include, for example, liquid triglycerides, polyethylene glycols, or paraffin hydrocarbons.
Suitable formulations for parenteral administration include aqueous solutions of the active compounds in water-soluble form, for example, water-soluble salts and alkaline solutions. In addition, suspensions of the active compounds as appropriate oily injection suspensions may be administered. Suitable lipophilic solvents or vehicles include fatty oils, for example, sesame oil, or synthetic fatty acid esters, for example, ethyl oleate or triglycerides or polyethylene glycol-400 (the compounds are soluble in PEG-400). Aqueous injection suspensions may contain substances which increase the viscosity of the suspension include, for example, sodium carboxymethyl cellulose, sorbitol, and/or dextran. Optionally, the suspension may also contain stabilizers.
The characterization of NMDA subunit binding sites in vitro has been difficult because of the lack of selective drug ligands. Thus, the compounds of the present invention may be used to characterize the NMDA subunits and their distribution. Particularly preferred subtype-selective NMDA receptor antagonists and agonists of the present invention which may be used for this purpose are isotopically radiolabelled derivatives, e.g., where one or more of the atoms are replaced with 3H, 11C, 14C, 15N, or 18F.
Electrophysiological Assays at NMDA Receptor Subunits
Preparation of RNA
cDNA clones encoding the NR1A, NR2A, NR2B, NR2C and NR2D rat NMDA receptor subtypes were provided by Dr. P. H. Seeburg (see, Morivoshi et al., Nature (Lond.) 354:31-37 (1991); Kutsuwada et al., Nature (Lond.) 358:36-41 (1992) Monyer et al., Science (Washington. D.C.) 256:1217-1221 (1992); Ikeda et al., FEBS Lett. 313:34-38 (1992); Ishii et al., J. Biol. Chem. 268:2836-2843 (1993) for details of these clones or their mouse homologs). The clones were transformed into appropriate host bacteria and plasmid preparations were made with conventional DNA purification techniques. A sample of each clone was linearized by restriction enzyme digestion and cRNA was synthesized with T3 RNA polymerase. The cRNA was diluted to 400 ng/xcexcl and stored in 1 xcexcl aliquots at xe2x88x9280xc2x0 C. until injection.
The Xenopus oocyte Expression System
Mature female Xenopus laevis were anaesthetized (20-40 min) using 0.15% 3-aminobenzoic acid ethyl ester (MS-222) and 2-4 ovarian lobes were surgically removed. Oocytes at developmental stages IV-VI (Dumont, J. N., J. Morphol. 136:153-180 (1972)), were dissected from the ovary still surrounded by enveloping ovarian tissues. Follicle-enclosed oocytes were micro-injected with 1:1 mixtures of cRNA:NR1A+NR2A, 2B, 2C or 2D; injecting xcx9c2,5, or 20 ng of RNA encoding each receptor subunit. NR1A encoding cRNA was injected alone at xcx9c20 ng. Oocytes were stored in Barth""s medium containing (in mM):NaCl, 88; KCl, 1; CaCl2, 0.41; Ca(NO3)2, 0.33; MgSO4, 0.82 NaHCO3, 2.4; HEPES 5, pH 7.4, with 0.1 mg/ml gentamicin sulphate. While oocytes were still surrounded by enveloping ovarian tissues the Barth""s medium was supplemented with 0.1% bovine serum. Oocytes were defolliculated 1-2 days following injections by treatment with collagenase (0.5 mg/ml Sigma Type I for 0.5-1 hr) (Miledi and Woodward, J. Physiol. (Lond.) 416:601-621 (1989)) and subsequently stored in serum-free medium.
Electrical recordings were made using a conventional two-electrode voltage clamp (Dagan TEV-200) over periods ranging between 3-14 days following injection. (Woodward et al., Mol. Pharmacol. 41:89-103 (1992)). Oocytes were placed in a 0.1 ml recording chamber continuously perfused (5-15 ml minxe2x88x921) with frog Ringer""s solution containing (in mM):NaCl, 115; KCl, 2; CaCl2, 1.8; HEPES, 5; pH 7.4. Drugs were applied by bath perfusion. Using oocytes expressing different subunit combinations of NMDA receptor, NMDA currents were activated by co-application of glutamate and glycine. Inhibitory potency of the novel antagonists was assessed on responses elicited by fixed concentrations of glutamate and glycine, by measuring reductions in current induced by progressively increasing concentrations of antagonists.
Concentration-inhibition curves were fit with equation 1.
I/Icontrol=1/(1+([antagonist]/10xe2x88x92pIC50)n)xe2x80x83xe2x80x83Eq. 1
in which Icontrol is the current evoked by agonists alone, pIC50=xe2x88x92log IC50, IC50 is the concentration of antagonist that produces half maximal inhibition, and n is the slope factor. (De Lean et al., Am. J. Physiol. 235:E97-E102(1978)). For incomplete curves analysis by fitting was unreliable and IC50 values were calculated by simple regression over linear portions of the curves (Origin: Microcal Software).
Maximal Electroshock-induced Seizures
Seizures were induced by application of current (50 mA, 60 pulses/sec, 0.8 sec pulse width, 1 sec duration, d.c.) through saline-coated corneal electrodes using a Ugo Basile ECT device (Model 7801). Mice were restrained by gripping the loose skin on their dorsal surface, electrodes were held lightly against the two cornea, then current was applied and mice were observed for a period of up to 30 sec for the occurrence of a tonic hindlimb extensor response. A tonic seizure was defined as a hindlimb extension in excess of 90 degrees from the plane of the body. Results were treated in a quantal manner.
The examples which follow are intended as an illustration of certain preferred embodiments of the invention, and no limitation of the invention is implied.